Turbochargers for gasoline and diesel internal combustion engines are devices known in the art that are used for pressurizing or boosting the intake air stream, routed to a combustion chamber of the engine, by using the heat and volumetric flow of exhaust gas exiting the engine. Specifically, the exhaust gas exiting the engine is routed into a turbine housing of a turbocharger in a manner that causes an exhaust gas-driven turbine to spin within the housing. The exhaust gas-driven turbine is mounted onto one end of a shaft that is common to a radial air compressor mounted onto an opposite end of the shaft and housed in a compressor housing. Thus, rotary action of the turbine also causes the air compressor to spin within a compressor housing of the turbocharger that is separate from the turbine housing. The spinning action of the air compressor causes intake air to enter the compressor housing and be pressurized or boosted a desired amount before it is mixed with fuel and combusted within the engine combustion chamber.
In a turbocharger it is often desirable to control the flow of exhaust gas to the turbine to improve the efficiency or operational range of the turbocharger. Variable geometry turbochargers (VGTs) have been configured to address this need. A type of such VGT is one having a variable or adjustable exhaust nozzle, referred to as a variable nozzle turbocharger. Different configurations of variable nozzles have been employed in variable nozzle turbochargers to control the exhaust gas flow. One approach taken to achieve exhaust gas flow control in such VGTs involves the use of multiple vanes, which can be fixed, pivoting and/or sliding, positioned annularly around the turbine inlet. The vanes are commonly controlled to alter the throat area of the passages between the vanes, thereby functioning to control the exhaust gas flow into the turbine.
Conventional vanes used with VGTs are shaped having a straight vane profile that is designed to provide an airfoil shape that is configured to both provide a complementary fit with adjacent vanes when placed in a closed position, and to provide for the passage of exhaust gas within the turbine housing to the turbine wheel when placed in an open position. Thus, the use of such straight vanes function to control a throat area of turbine housing, thereby operating to control the boost delivered by the turbocharger. However, such straight vanes are only able to provide a well-distributed flow of exhaust gas to the turbine wheel within a small range of the total use, thereby not contributing to the most efficient turbocharger operation.
It is, therefore, desired that the vanes used with a variable geometry turbochargers be specially configured in a manner that broadens the desired gas flow distribution window, thereby operating to facilitate and promote efficient turbocharger operation. It is also desired that such vanes be designed in a manner that facilities use of the same within variable geometry turbochargers with minimum adjustments or retrofit changes.